Instantiating variables in Controller on start of application using Play Framework

I am using Java through the Play Framework to implement an API. I am trying to instantiate a few variables on the start of the application that should last for the entire life of the application and that are to be used in my HomeController.
These variables are objects that can be used to call functions from a specific class.

I have read that the best way to implement code that executes on the start of the application is to use Dependency Injection but I did not understand how to do it.